Furnace



H. P} FORD Aug. 13, 1935.

FURNACE Filed April 24, 1950 5 Sheets-Sheet l.

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INVENTOR fi ra/a/ P fZraf TTORNEY Aug. 13, 1935.

H. P FORD F-URNACE Filed April 24, 1950 5 Sheets-Sheet 2 Nun."

if! TTORNEY Aug. 13, 1935. R FORD 2,010,985

FURNACE Filed April 24, 1930 5 Sheets-Sheet 3 INVENTOR Harv/a I- O/"dATTORN EY H. P. FORD Aug. 13, 1935.

FURNACE Filed April 24, 1930 5 Sheets-Sheet 4 INVENTOR BY Ham/d P Fara.

A TORNEY H. P. FORD 2,010,985

FURNACE Filed April 24, 1930 5 Sheets-Sheet 5 Aug. 13, 1935 Q E 5?? 08Go 8o 00 o C 00000 000 oo womvo 0000 000 000000 00000000 000000 0000000000000 00000000 0000 00 0000 000000 0000 0000000 000000 oooooooo oooooooo 00 000 00 0000 00000000 000000 0000 000 000000 00000000 000000 00000000 0000 f I i N\\ \&

INVENTOR BY Ham/0 Pfara ATTORNEY Patented Aug. 13, 1935' UNITED i S TATES FURNACE 7 Harold P. Ford, Seattle, Wash. 7 Application April 24.1930', Serial-No. 447,024

8 Claims.

My invention relates to furnaces and the general object of my inventionis to provide a furnace of improved construction which will pro duce amore complete and'efficient combustion of the fuel and which willutilize a maximum amount of the heat derived from the fuel combustion.

In furnaces of the type now in common use it is common practice to allowthe gases produced by combustion of the fuel to escape up the chimney ina partially burned and a relatively hot condition. This is undesirableand results in low efficiency, because the availableheat in the gaseshas not all been liberated by complete combustion, and because the heatwhich has been liberated has not, all been used, and because the partlyburned gases carry with them much soot and smoke which tend to foul thepassageways in. the furnace and chimney and which are a nuisance and asource of dirt when released in the atmosphere. Other objections to theusual types of furnace are that large volumes of cold air are oftendrawn through the open furnace door or through cold spots of the fuelbed into the furnace and brought into contact with and chilling the heatabsorbing devices, and that the heat absorbing or pick up devices areoften placed within the hottest, portion of the combustion chamber, thustending to re.- duce the temperature within the combustion chamber totoo low a degree for'completecombustion.

My invention overcomes the objectionable features hereinbefore set forthby providing for a re-circulation of thefuel gases through the fuel bedand combustion chamber and past heat absorbing means'until substantiallyall of the combustible matter is burned andsubstantially all of the heatis absorbed out of these gases before they are allowed to dischargethrough the chimney. To accomplish this, I use? what I term arecirculation principle in which the gases resulting from combustion arere-circulated through the fire box and combustion chamber untilsubstantially all of the volatile matters are burned or oxidized.- Incarrying out this re-circulation principle, I provide a refractory firebox in which a very hot bed of coals either large or small may bemaintained and provide a refractory combustion chamber in directconnection with this fire box which is maintained at a high temperatureand which is not cooled by the presence therein, or close proximity ofheat take off means. The fire box and combustion chamber, together withth space im d at y b low the fire box constitute what I term the hot legof a recirculation system in which the gases rise or flow upwardly andin which said gases and preheated air are brought into intimate contactwith the fuel and are retained in highly heated chambers long enough toeffect substantially perfect combustion. The heat pick up meansconstitutes the coldleg of this re-circulation system and is arranged toreceive the highly heated gases after they leave the combustion chamberand extract the heat from said gases; The general direction of flow ofthe gases in the hot leg of the circuit is upward and their velocitywill varywith the temperature and may be influenced by introduction offresh air under pressure. The general direction of flowof the gases inthe cold leg of the circuit is down to a point below" the fire box andthence up again'through the hot leg of the circuit. A portion of thesegases is allowedto pass off constantly into a vent which leads to achimney, the location v liere these gases are taken off being the lowestpart of the circuit or the location at which the gases pass from thecold leg into the hot leg of said circuit. Fresh air, preferablypreheated, may be admitted at various parts of the. recirculationcircuit but is preferably introduced from a blast chamber or admission,chamber through the zone where initial and hottest burning of the fueltakes place, and thence mixing with'the recirculation gases. A forcedair admission may be used but such is not essential to the operation ofthe furnace as the gravity circulation in the hot and cold legs of thefurnace is ample to overcome all internal friction and the resistance ofthe fire bed, and the external chimney need only serve as a vent stackto elevate the waste gases to a point of discharge. The closed circuitthrough which the gases travel brings said gases into effective. contactwith the lowest as well as the highest portion of the heat pick upmeans. When the fire box is chilled as by leaving open the fire boxdoor, the gravity circulation is retarded or stopped, thus preventingsaid heat pick up means from being subjected to cold blasts or drafts ofair. Checking of the draft does not hinder the flow of 're-circulationgases in the closed circuit but may reduce the amount of gas dischargedthrough the chimney. The high state of combustion of the fuel tends toprevent fouling of the surfaces with which the burned gases come intocontact andthe downward movement of the gases in the cold leg of I thecircuit tends to cause any small particles of ash or solid matter insaidgases to be deposited in the ash pit. Fire hazard is greatly reduced byhaving the gases comparatively cool before they discharge into thechimney.

More specific objects of my invention are to provide a furnace of neatand attractive appearance, which is compact in construction, low infirst cost and upkeep and occupies a relatively small floor space; toprovide a furnace which will not be liable to be damaged by overheatingor unequal expansionstrains; to provide a force feed furnace having animproved form of grate which will burn low grade, cheap and fine coalefficiently, which will not drop the fine coal and which will keep thebed of burning coal broken up and evenly distributed over the grate atall times thus preventing the formation in the bed of coal of dead spotsand air channels through which large volumes of air can pass withoutcoming into intimate contact with the coal. Another specific object isto provide a furnace in which the re-circulation air is caused to passthrough the ash pit whereby it may pick up the heat of the dischargingashes.

In certain types of furnaces now in use, fans, injectors and othermechanical means have been used to re-circulate a portion of the chimneygases through the fire bed or fire zone for the purpose of a morecomplete combustion of the products from the fuel. This necessitates amore expensive and complicated installation.

As ordinarily employed, this return or recirculation of the gases bymeans other than by gravity is not well suited to the varying conditionsof temperature and combustion within the furnace or fire zone, and doesnot permit satis factory operation and control.

The gravity re-circulation principle returns the gases in a quantity inproportion to the temperature within the fire zone. In other words, withhigh firebox temperatures, a greater portion of return is automaticallyproduced, and with low firing rate and low temperature in the fire box,a smaller portion of return gases is produced, which is satisfactory forpractical operation of the furnace. If fan or other mechanical means, asdifferentiated from gravity, be employed to return or re-circulate aportion of the chimney gases, this desired ratio is not maintained.

The above mentioned general objects of my invention, together withothers inherent in the same, are attained by the device illustrated inthe following drawings, the same being preferred exemplary forms ofembodiment of my invention, throughout which drawings like referencenumerals indicate like parts:

Figure 1 is a vertical sectional view substantially on a broken lineI--l of Fig. 2 of a domestic hot air furnace constructed in accordancewith my invention;

Fig. 2 is a vertical section of the same substantially on broken lineZ-2 of Fig. 1;

Fig. 3 is a cross section substantially on broken line 3-3 of Fig. 1;

Fig. 4 is a vertical mid-section on a broken line 44 of Fig. 5 of a hotwater furnace constructed in accordance with my invention;

Fig. 5 is a cross section substantially on broken line 5-5 of Fig. 4;

constructed in accordance with my invention,

said furnace being substantially identical with the hot water furnaceshown in Figs. 4 to 7 except that a steam drum is provided in connectiontherewith;

Fig. 9 is a front elevation of said steam furnace;

Fig. 10 is a side elevation of said steam furnace;

Fig. 11 is a fragmentary sectional view on a larger scale illustratingwall and door construction embodied in my furnace;

Fig. 12 is a fragmentary-plan view on a larger scale of a portion of thegrate or tuyere used in the bottom of my fire box;

Fig. 13 is a fragmentary sectional view substantially on broken linel3-l3 of Fig. 12;

Fig. 14 is a detached view partly in elevation and partly in section ofone form of automatic fuel feed device which may be used in connectionwith my invention;

Fig. 15 is a View partly in end elevation and partly in sectionsubstantially on broken line [5-45 of Fig. 14 of said automatic fuelfeed device;

Fig. 16 is a vertical sectional view showing my invention embodied in arelatively large steam boiler;

Fig. 17 is a fragmentary sectional view substantially on broken linel'l--ll of Fig. 16; and

Figs. 18 and 19 are fragmentary cross sectional views substantially onbrokenlines l8-l8 and l9i9 of Fig. 16. 7

Referring first to the hot air furnace, as disclosed in Figs. 1 to- 3inclusive, I show a furnace of a type suitable for domestic useembodying an outer metal housing 2 having a convergent top end 3arranged to be connected with a plurality of heat distribution pipes iwhich may extend to the rooms or other areas to be heated. The cold airis admitted through an opening 4 to a compartment 5 in the lower rearportion of the furnace and flows upwardly as indicated by arrows A, in amanner hereinafter described.

The side of the furnace shown at the left in Fig. l and hereinaftertermed the front side, is provided with an upper removable wall sectionB and with a fire pot door 1 and with an ash pit door 8. The wallsection 6 is preferably in the nature of a slab of refractory materialcast into a metal casing 9 which extends over the outer surface and overthe edges thereof, said edges preferably being inclined, as shown, toprevent displacement of the refractory slab. The door 1, which is moreclearly shown in Fig. 11, is a slab of refractory material cast in asimilar manner in a metal casing and said door is secured as by bolts IDto a metal door plate H which is connected by hinges l2 to a wall i3.The bolts 56 extend through enlarged holes M in the door plate H wherebythe position of the door slab l on the plate H may always be adjusted tofit snugly within the door opening, the nuts on said bolts being on theoutside where they are readily accessible for the purpose of adjustmentand serv- 'ing to clamp the door slab firmly to the door plate in anydesired position. All of the doors and wall sections in all forms of myinvention herein disclosed are preferably of substantially the same'form of construction. The refractory slabs are preferably secured tothe metal casings within which they are placed by anchor bolts !5 havingconical heads 56 seated within the metal plates and having large flatnuts H which are embedded within the refractory slabs all as moreclearly is shown in Fig. 11. All sections forming the outer .wallsof thefurnace are preferably flanged outfire box and the grate beingpositioned toward form the ends of the fire box. From the abovedethefront. The grate l9 may be formed of overlapping spaced apart angle barsextending crosswise of the fire boo: and stepped or inclined downwardlyfrom rear toward the front. A dump plate 2| is provided at the frontedge of the fire box to catch the ashes which pass over the grate l9.This dump gate is preferably connected with a weight or spring, notshown, and is arranged'to dump automatically when sufficient weight ofashes has accumulated thereon. It may also be dumped by hand. The blastbox, which is shown on a larger scale in Figs. 12 and 13, may be ofvaried size and shape, and is capable of preheating the air which passesthrough it and of keeping the fuel broken up enough to allow the air topass freely through said fuel. A preferred form of blast box, as shownin the drawings may be constructed with an air tight bottom wall 22,

7 an upwardly inclined front portion 23 and a rear portion 24 whichextends upright for a short distance and is thence inclined forwardly"for a short distance sothat the incoming fuel may first pass over thisinclined portion and then over a plurality of tuyere members 25. Thetuyres 25 may be transversely disposed overlapped, spaced apart, anglebars with their openings di rected forwardly as shown, or'said tuyeresmay be of a different form of construction so long as their openings areturned away from the direction of movement of the fuel whereby they willnot be liable to become clogged by the fuel. Air is admitted to theblast box through a plurality of nozzles 5! which are connected with anair inlet pipe 52. Either a gravity or forced circulation of air may beused. This air is preheated in the blast box before iii-discharges fromthe tuyeres. The front portion 23 of the blast box terminates at asubstantial distance above the grate I3 and forms a lip so that therewill be a cascading or falling of the fuel where it passesonto thegrate. In addition to this, spurs 28 may extend above the edge of thelip portion 23 to break up the partly burned fuel at this location andpermit the air to pass freely through thefuel and come into intimatecontact with said fuel at this point. The more intense burning of thefuel is done as it passes over the blast box and the final and lessintense burning is done as the fuel passes over the grates IS. The angleor pitch of the grates l9 from rear to front, may be varied to suitdifferent requirements and different kinds of fuel. The spacing of thegrate bars and of the tuyre members may be varied to suit differentrequirements.

The rear side of the fire box may be formed by a slab 21 of refractorymaterial and the top rear wall of said fire box above the blast box, isformed by another slab 28 of refractory material which is. inclinedupwardly from rear to front, as shown Two refractory end slabs 29scription it will be seen. that the fire box. is substantiallytriangular in cross section and is lined throughout the greater portionof its area'with refractory material which helps to maintain a hightemperature within said fire box.

Fuel is supplied to the rear of the fire box througha feed tube 3|having a. feed screw 3i therein. 3 i An upright combustion chamber 32preferably formed of a refractory member 33 of rectangular cross-sectionis provided directly above the front'endofthe'fire boxand adjacent tothe front. wall 6 of the furnace. This refractory member 33 may be ofone piece construction as shown, or it maybe of multiple piececonstruction. The purpose of this combustion chamber is to provideadditional space through which the gases from the fire box may flowwhile a high temperature is maintained and i where a more completecombustion of'the gases may be obtained, additional time forthis'combustion being afforded in this highly heated refractory combustion chamber. This combustion chamber together with the fire box andash pit provide what I term an internal chimney or the hotter leg of are-circulationsystem for the gases.

At the top end of the combustion chamber 32, I provide a curveddeflector plate 33' for directing the hot gasesrearwardly to the heatabsorbing means. Thisheat absorbing means in the hot air furnace, ispreferably in the nature of spaced apart plates 34 of heat transmittingmetal, as thin steel, connected at their edges by similar strips ofmetal 35 'sothat they present a deeply corrugated appearance, when seenin cross section, as in Fig. 3,and so that they form one series orgroupof spaces 36 through which the heated gases may pass downwardly andanother series of spaces 31 through which the air that is being heatedmay pass upwardly. This gives a very large heat transmitting area wherethe ases may give up their heat and the air may pick up this heat. Theplates 34 may be upright or substantially upright and substantiallyparallel, and are preferably smooth on the side where they pick up theheat and roughened on the side where they give up the heat to increasetheir heat transmitting capacity.

The air transmission spaces 31 are open at their rear edges andcommunicated with a space 38 within the furnace housing 2 and the frontedges of said spaces 31 are closed by the walls 35, which are spaced farenough from the wall of the combustion chamber 32 to afford room for acoil 39 of hot water tubes, and which are inclined rearwardly toward thebottom and above the inclined refractory fire box wall 28 to afford roomfor a soot blower tube 40 through which a blast of sand and air may bedischarged into the heated gas passageways 35 to keep the plates 34 freefrom carbon and soot and thus prevent reduction of their heattransmitting capacity. The soot blower tube 4!) is mounted so that itmay be rotated .from the exterior of the furnace through part of onerevolution to clean all parts of the plates 34. The sand discharged fromthe soot blower discharges into the ash pit.

After passing down through the heat pick up passageways 38, the gasesdescend through a passageway 4| into a chamber 42 in the ash pit 43. Inits travel through the passageway 4| the still warm gases come incontact with the fuel inlet tube 30 and preheat the fuel before itenters the fire box. In the chamber 42 a portion of the ases passesthrough a slot 44 into a smoke pipe 45 and discharge and the remainderof said gases passes upwardly once more through the grate I 9 and thefuel bed and mix with the freshly introduced air and re-circulate inthemanner heretofore described."

The ash pit 43 is preferably depressed below the fioor on which thefurnace rests to afford suflicient depth for the reception of arelatively large ash can 46 which may be removed through the door 8 andthrough thespace afforded by the removal of a horizontal door 8' thusmaking possible the removal of the ashes without shoveling. A hopper 53is provided for the reception of an adequate supply of fuel.

The air which is to be heated is admitted through the opening l into thecompartment 5. Thence it may pass over a humidifying device in thenature of a plurality of shallow overflow pans 4'! having water therein.Said air then passes upwardly through a passageway 48 and through theheat pick up spaces 31 and is conveyed by the pipes l to the rooms orarea to be heated. Water for the humidifier pans 41 may be admittedthrough a pipe 49 and receptacle 49' and any excess or overflow watermay discharge into a receptacle 5B which is provided with a suitableoutlet. The fuel inlet tube 30, where it extends through the fresh airpassageway 48, is preferably enclosed within a jacket 38 to preclude anypossibility of contamination of the fresh air by smoke and gases, and,for the same reason, all parts separating the gas and combustionchambers from the air passageways are of gas tight construction.Suitable check drafts and dampers are necessarily provided in the smokepipe 45 outside of the furnace.

In the operation of this furnace a large propor tion of the combustiongases is constantly recirculated and a small amount of these gases istaken off constantly through thesmoke pipe $5. This re-circulation ofthe combustion gases under the conditions described, insures a maximumeificiency in combustion of the fuel and prevents an obnoxious dischargeof soot and heavy smokeinto the atmosphere.' The ash pit chamber 42together with the fire box i8 and the combustion chamber 32 constitutethe hot leg or ascending internal chimney and the spaces 36 andpassageway constitute the cold leg or descending section of myre-circulation system.

The hot water furnace shown in Figs. 4 to '7 in clusive is the same asthe previously described hot air furnace so far as the ash pit, gratesand blast box, fuel feed, fire box and combustion chamber are concernedand the same reference numerals and descriptive matter are applied tothese parts. This hot water furnace differs from the hot air furnaceessentially in the fact that hot water tubes 5% are provided in the heatpick up space at the rear of the combustion chamber and are connectedwith an upper header or receptacle 55 and a lower header 56. Thecirculation of the heated gases in this type of furnace will be thesameas previously described in connection with the hot air furnace. Thegravity circulation. of the water will be into the lower header 56through a conduit 56 thence through the pipes 54 in the directionindicated by the arrows to the upper header 55, thence out to anysuitable device to which the hot water is to be delivered through outletconduit 55. In this form of construction the soot blower pipe 40' islocated at the common center of the pipes and is arranged to deliversand and air for keeping said pipes clean. The headers 55 and 56 arepreferably insulated by refractory material as at- 5'! to help conserveheat and extra slabs of insulating material are provided at the sides ofthe heat pick up chamber, as indicated at 58in Figs. 5 and 6, and at thetop of said heat pick up chamber as indicated at 59 in Fig.4; A block 60of'refractory material replaces the plate 33 shown in Fig. l.

The operation of this form of the invention is the same as the operationof the form shown in Fig. 1 except that water instead of air is heated 1by the hot gases from the combustion chamber.

In Figs. 8, 9 and 10, I show a steam drum 6| mounted above the furnaceand connected by pipes 62 with the return conduits 56' and by pipes 63with the outlet conduits 55. When the steam drum is thus provided steamwill collect in said drum BI and the'device may be used in a steamheating system.

Figs. 8, 9 and 10 also show a forced circulation means for supplying airto the soot blower pipe 40 or ll) and to'the pipe 52 which furnishes airto the blast box, said air being supplied through pipes 64 and 65 whichare connected with a fan or blower 66. A split damper til is provided atthe junction of the pipes (i l and 65 for selectively directing anydesired proportion of the air which is delivered by the fan into eitherone of said pipes; The pipe 65 also has an opening to the. atmospherewhich is arranged to be regulated by a damper Bl whereby when saiddamper iii is opened a gravity circulation may be maintained through theblast box pipe 52 in the event the blower 66 is not operating. When aforce draft is to be used continuously the blower 56 will ordinarily bedriven by a motor, not shown, but when no continuous source of power isavailable said blower may be operated by hand to start, or speed up thefire or to deliver a blast to the soot blower, and the operation of thedraft portion of the furnace may otherwise be by gravity. It will beunderstood that this draft and blower system may be used on the hot airfurnace shown in Figs. 1 to 3.

In Figs. 14 and 15, I have shown, in detail, one form of hydraulic motorwhich may be used to operate the fuel feed of my furnace, it beingunderstood that any other desired form of power actuated mechanism maybe used for this purpose. When this device is thus utilized I provide aratchet wheel 88 on the shaft 3| of the worm 3!, see Fig. 4,and'preferably provide two pawls 69 and 10 for rotating said ratchetwheel in the direction indicated by the arrow in Fig. 14. These pawlsare totally independent of each other in their operation, one of saidpawls 69 being pivotally mounted on a hand lever H which may bereciprocated by hand for speeding up the delivery of the fuelinto thefire box and the other pawl '75 being-pivotally mounted on a power lever12 which is connected by a slot and pin connection 13- with-a piston rodM. A hydraulic piston 15 on one end of the rod '58 is reciprocablydisposed within a-cylinder 1B; A compression spring "H is provided onthe other end of the rod kl between a cross pin and washer l8 on the rodand a rigid frame bracket '19. The cylinder l5 and frame bracket iii areboth rigidly mounted on the same frame piece 88, the arrangement beingsuch as to allow the piston to move the rod l to the left from theposition shown in Fig. 14 and the spring to return said rod by moving itto the right when fiuid pressure behind the piston is released. Waterunder pressure for moving the piston 15 is admitted to the end ofcylinder it through a pipe 8| having a three way valve 82 therein. Whenthe valve member is in the position shown in Fig. 14 water underpressure is free to enter through a supply pipe 81' but when the valvemember is moved clockwise througha substantial angle, as bymoving thelower end of a crank arm 533, which is connected with said valve, frompoint E to point F, then the port of the supply pipe 8lf will be closedand pipe 81 will be connected with a discharge or exhaust pipe -84. Thelower end of the crank arm 83 is pivotally-connected by a link 85 withone end ofa reciprocable member 8S5 which is slidably mounted inbrackets 87 and adapted to be moved by a flat spring 88 which is securedto the lever 12. A stud bolt 89 issecured to the frame piece 8-0 in thepath of movement of the end of the spring 88 and is preferablyadjustable in a direction crosswise of the frame piece 80 to vary thedistance which the arm 12 will have to move past center in order to snapover the stud bolt 89, strike the member, 86 and throw the valve. Fig.14 shows the several parts in the position they would occupythe instantafter the spring 88 had snapped over the stud pin 35 and opened thevalve 82 .to intake as the lever 72 moved toward the right. As soon asthis opening movemen-t of the valve occurs the water pressure begins tomove: the piston 75 to the leftcarrying with it the lever J 2 androtating the ratchet wheel clockwise. When the lever arm 12 issubstantially vertical the end of the spring 88 strikes against the studpin 8-9 but the arm 12 continues to move on to the left until the spring88 has flexed enough to slip over the top of. the stud pin, strike themember 86 and move said member to the left thus closing the valve '82 tointake and opening the same to exhaust, whereupon the spring I7 beginsto move the piston 15, and parts connected there with back toward theposition shown in Fig. 14. By adjusting the position of the stud pin 89vertically, the length of stroke may be increased or decreased and bygoverning the rate of flow through either or all of the pipes 81, 81',82, the speed of movement of the piston '15 and connected parts may bevaried. The levers H and 72 may be forked or may be in duplicate on bothsides of the ratchet wheel 53 as shown in Fig. 15. The application ofthe hydraulic feed means shown in Figs. 14 and 15 is indicateddiagrammatically in Fig. 9. This hydraulic means forms a relativelycheap, simple efficient and reliable device for operating the automaticfuel feed but it will be understood that other power operated means maybe used for this purpose.

In Figs. 16, 1'7, 18 and 19, I have shown my invention as embodied in arelatively large steam boiler or heating plant. In this installation Iprovide a furnace housing 90 of refractory material which may be dividedby partitions 90 to form a plurality of separate fire boxes SI andcombustion chambers 92. The grates l8 and blast boxes 20 in each ofthese compartments are similar to the corresponding parts hereinbeforedescribed both in construction and mode of operation. A power operatedtraveling ash discharge conveyor 93 may replace the ash can 46 thusautomatically taking care of the ashes and reducing the necessity for alarge ash pit. The heat pick up devices are located in the same relativeposition as previously described and comprise a multiplicity of uprightor slightly inclined water tubes 96 connected at their upper end with asteam drum 95 and at their lower end with. a water drum 96 and a muddrum Scot blower nozzles Ml are provided for keeping the water tubesclean and feed screws 3| are provided for delivering fuel into the rearend of each fire box. Fresh air, preferably from a blower, not shown,enters through a common chamber 98, thence passes through pipes 99 and99 to the blast boxes 20'. The pipes 99 extend through the exhaust ventHill which may be connected with a chimney not shown, and the pipes 99extend through the passageway by which the re-circulation gases returnto the chamber below the grate. In this way the fresh air is preheatedbefore it reaches the blast box. The re-circulation gases are split by adamper HH and any desired proportion of. said gases are allowed topassoutwardly through the vent I00. The operation of the furnace shownin Figs. 17 to 20 is substantially the same as the operation of thepreviously described furnaces, in so far as the principle .ofre-circulation of the gases and combustion of the fuel is concerned.

By employing this principle of re-circulation of the gases and ofmaintaining a high temperature in the fire box and combustion chamber, Iam able to produce a furnace in which the combustion of the fuel issubstantially complete and the heating efficiency is greatly increased,and undesirable smoke and soot are substantially done away with.

Obviously, changes may be made in the form, dimensions and arrangementof the parts of my invention, without departing from the principlethereof, the above setting forth only a preferred form of embodiment.

I claim:

1. A furnace embodying a fire box; an ash pit chamber below said firebox; a combustion chamber-communicating with the upper portion of saidfire box; a heat pick up chamber communicating withthe upper portion ofsaid combustion chamber and with said ash pit chamber andcooperatingwith said fire box and said combustion chamber and said ash pit chamberto .form a closed circuit for the re-circulation of heated gasesresulting from combustion; walls of heat insulating refractory materialseparating said heat pick up chamber from said fire box and saidcombustion chamber whereby coolingof the gases in said fire box and saidcombustion chamber is prevented; means for admitting fresh air at thelower portion of said fire box and means within said ash pit chamber forwithdrawing a portion of said re-circulated gases.

2. A furnace embodying a fire box; a combustion chamber communicatingwith the upper portion of said fire box; an ash pit chamber below saidfire box; a heat pick up chamber at one side of said combustion chamber,said heat pick up chamber communicating with said ash pit chamber andwith the upper end of said combustion chamber and cooperating with saidcombustion chamber and said fire box and said ash pit chamher to form aclosed circuit for the re-circulation of gases, walls of heat insulatingrefractory material separating said heat pick up chamber from said firebox and said combustion chamber whereby cooling of the gases in saidfire box and said combustion chamber is prevented and a difference intemperature in said two chambers sufficient to produce a gravitycirculation of gases upward in said combustion chamber anddownward insaid heat pick up chamber is obtained, heat pick up means in said heatpick up chamber, flue means in said ash pit chamber for withdrawing aportion of said re-circulation gases; and means in said ash pit chamberfor admitting fresh air to said fire box.

3. A furnace embodying a fire box; a grate forming the bottom of saidfire box; a blast box forming a tuyere in said grate; a tubularchimney-like member forming a combustion chamber above said fire box andcommunicating with said fire box, said fire box and said combustionchamher constituting an internal chimney through which heated gases mayascend; means forming a heat pick up chamber communicating with theupper end of said combustion chamber and with the space below saidgrate, whereby said gases may descend through said heat pick up chamberand again pass upwardly through said fire box and said combustionchamber; fiue means for withdrawing a portion of said gases from thespace below said grate; means for feeding fuel into said fire box oversaid blast box; and means fdr delivering fresh air into said blast box.

4. A furnace embodying a fire box; an inclined grate forming the bottomof said fire box: a blast box at the side of said grate, said blast boxhaving tuyre openings therein; force feed means for delivering fuel intosaid fire box onto said blast box; means for delivering fresh air tosaid blast box; means forming a combustion chamber above said fire boxand communicating with the same; means forming a heat pick up chamber atthe side of said combustion chamber for receiving heated gases from thetop of said combustion chamber and passing said gases downwardly to thespace below said grate whereby a portion of said gases may re-circulateupwardly through said grate; and vent means below said grate forwithdrawing a portion of said gases.

5. The apparatus as claimed in claim 4 in which said fire box has aninclined top wall of refractory heat insulating material extending oversaid blast box and forming a banking roof above said blast box.

6. The apparatus as claimed in claim 4 in which the inclined grate isformed of a plurality of overlapping spaced apart plates for preventingthe passage of fine fuel therethrough and in which a dump plate isyieldingly supported for swinging movement at the lowermost forward edgeof said grate to dump by gravityin response to the pres ence of a loadof ashes thereon.

a blast box at the rear side of said grate; means forming tuyereopenings in the top of said blast box; an upwardly extending lip at theforward edge of said blast box over which fuel may drop downwardly ontosaid grate; spurs on said lip for breaking up said fuel; power operatedfeed means for forcing fuel into the rear of said fire box and movingsaid fuel over said blast box; means for delivering fresh air to saidblast box; means forming a combustion chamber above said fire box andcommunicating with the same; means forming a heat pick up chamber at theside of said combustion chamber for receiving heated gases from the topof said combustion chamber and passing said gases downwardly to thespace below said grate whereby a portion of said gases may recirculateupwardly through said grate; and vent means for withdrawing a portion ofsaid gases below said grate.

8. A furnace embodying a fire box; a grate in the bottom of said firebox; a feed chute entering one side of said fire box; means for feedingfuel through said chute into said fire box; means forming a combustionchamber above said fire box and communicating therewith; means forming aheat pick up chamber communicating with the space below said grate andwith the upper portion of said combustion chamber whereby heated gasesmay pass downwardly through said heat pick up chamber and be returned tosaid fire box, said feed chute passing through said heat pick up chamberwhereby fuel therein will be preheated before entering said fire box;and vent means below said grate for withdrawing a portion of said gas.

HAROLD P. FORD.

